Air percussion drilling assembly for directional drilling applications

ABSTRACT

An air percussion hammer drill is disclosed for operation in an earthen formation. The air compression hammer mechanism comprises a piston that reciprocates while simultaneously rotating within its housing. A hammer drill bit slidably keyed to the bottom of the piston transfers the impact energy to the formation and rotates during operation independent of an attached drill string. The air percussion hammer assembly is therefore ideally suited to directional drilling activities.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to an air compression hammer drill bit fordirectional drilling operations. More particularly, this inventionrelates to an air compression hammer tool for directional drillingoperations. The hammer impacts while simultaneously rotates the bit,thereby assuring maximum penetration of the bit in an earthen formation.

2. Description of the prior art

In percussion drilling, the rock cutting mechanism is of an impactingnature rather than shearing. Therefore, the drill bit rotationalparameters, e.g. torque and rpm, are not relevant from a rock formationbreaking point of view, except for the necessity that the cuttingelements of the bit need to be "indexed" to fresh rock formations. Instraight hole air drilling, and especially in mining, this need isachieved by rotating the drill string slowly. This is accomplished inconventional hammer bit operations by incorporating longitudinal splineswhich key the bit body to a cylindrical sleeve at the bottom of thehammer (commonly known as the driver sub). The drill string rotation isthen transferred to the hammer bit itself. Experience has proven thatthe bit optimum rotational speed is approximately 20 rpm for an impactfrequency of 1600 bpm (beats per minute). This rotational speedtranslates to an angular displacement of approximately 4 to 5 degreesper impact of the bit against the rock formation. Another way to expressthis rotation is the cutters positioned on the outer row of the hammerbit move at the approximate rate of one half the cutter diameter perstroke of the hammer.

An example of a typical hammer bit connected to a rotatable drill stringis described in U.S. Pat. No. 4,932,483. The downhole hammer comprises atop sub and a drill bit separated by a tubular housing incorporating apiston chamber therebetween. A feed tube is mounted to the top sub andextends concentrically into the piston chamber. A piston is slidablyreceived within the housing and over the feed tube. Fluid porting isprovided in the feed tube and the piston to sequentially admit fluid ina first space between the piston and top sub to drive the piston towardsthe drill bit support and to a second space between the piston and thedrill bit support to drive the piston towards the top sub.

Rotary motion is provided to the hammer assembly and drill bit by theattached drill string powered by a rotary table typically mounted on therig platform.

The rotation of the drill string in the conventional hammer bitoperation described above, takes away the ability to turn, build, ordrop angles which are fundamental in directional drilling operations. Amethod to rotate the hammer bit without rotating the drill string isinstrumental in any directional drilling or steerable system. Such arotation can be accomplished by a motor mechanism positioned above thehammer that induces rotational motion to the bit itself.

The air percussion hammer tool taught in this specification hasparticular application for use with the technology taught in U.S. Pat.No. Re. 33,751 entitled SYSTEM AND METHOD FOR CONTROLLED DIRECTIONALDRILLING assigned to the same assignee as the present invention andincorporated hereby by reference. The patent teaches a system and methodfor controlled directional drilling utilizing a system approach todesign the hardware for drilling according to the well plan. The bendangle of a bent housing, connected between the bit and downhole motor,the diameter of a plurality of stabilizers and placement of thestabilizers with respect to the drill bit are selected and predeterminedon the basis of the desired well plan. With the use of an MWD, thedirection of the progressing borehole is tracked from the surface.Direction changes as required are controlled from the surface simply bycontrolling rotating of the drillstring. For curved path drilling, onlythe downhole motor or, the air percussion hammer of the presentinvention is rotated causing the borehole to travel along the curvedetermined by the bend angle in the bent housing and the diameter andlocation of the concentric stabilizers. When straight hole drilling isrequired, both the downhole motor or air percussion hammer and theentire drill string are rotated, effectively nullifying the effect ofthe bend angle in the bent housing.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an air hammer assembly thatimpacts and simultaneously rotates a hammer bit independent of a drillstring.

It is another object of this invention to provide a steerable airpercussion drilling assembly for directional drilling operations whereinthe hammer mechanism converts axial motion to rotary motion to anextended portion of the bit body as the bit works in a borehole.

The kinetic energy of the reciprocating piston is employed to rotate thebit. The linear motion of the piston is converted into rotational motionby using one or more helical grooves formed by the piston body. Toprevent the piston from oscillating in the rotary mode, an indexingclutch mechanism is provided to induce rotation of the bit in onedirection only.

The upper portion of the hammer bit (normally splined) is replaced by ashaft that is slideably engaged with and keyed to, a complimentarilyshaped female receptacle or bore formed by the lower portion of apiston. The shaft of the hammer is therefore, slideably engaged at alltimes, to the base of the piston and is so designed to be rotated by theindexing piston with a minimum of drag. Thus, axial motion between thepiston and bit body is allowed but relative rotational motion is not,i.e, the bit would rotate if the piston rotate and vice versa. One ormore longitudinal helical grooves are machined on the piston uppersection. These grooves are keyed to an inner race of a "sprag" clutchassembly via dowel pins or spherical balls. The outer race of thisclutch assembly is locked to the inner bore of a cylindrical hammerhousing. The clutch sprags are set to clockwise motion and to preventcounter clockwise rotational movement of the inner race with respect tothe outer race.

The downward motion of the piston, (the piston being coupled to theclutch through interaction between the helical groove, the engaged balland the clutch) mandates either a counter clockwise rotation of theinner race or a clockwise rotation of the piston. Since counterclockwise rotation of the inner race is not possible, the piston mustrotate clockwise when the piston moves downward. Similarly, the upwardmotion of the piston requires either the clockwise rotation of the innerrace or the counter clockwise rotation of the piston. Since the frictionagainst the clockwise rotation of the inner race is significantly lessthan that against the piston/bit rotation, the inner race would rotateclockwise and allows the piston to move straight upward. Therefore, onthe downstroke of the piston the bit is forced to rotate clockwise;while on the upstroke the inner race rotates instead, thereby preventingthe bit from "turning back".

An air percussion hammer apparatus with means for rotating the hammerbit while its piston reciprocates in a housing independent of anattached drill string is disclosed. The bit rotating means consists of acylindrical housing forming a first open up-stream end connectable to adrill string component and a second downstream end, the second endcontaining the hammer bit.

A pneumatic feed tube forms a first open end and a second substantiallyclosed end, the first end of the feed tube being concentric with andfixed within the housing. The feed tube is positioned toward the firstupstream end of the housing, the second end of the feed tube forms oneor more metered openings between the first and second ends of the feedtube.

A piston body is slidably retained within a first sleeve formed by thehousing. The piston body forms first and second open ends with the firstend being concentrically retained and slidably engaged with the secondend of the feed tube. The second downstream end of the piston forms ahammer striking surface. The piston further forms at least one axiallyoriented helical groove in an outside wall of the first upstream end ofthe piston and a pair of pneumatic communication ports between anoutside wall of the body and an interior chamber formed by the body.More specifically, one of the ports leads from an interior chamberformed by the piston toward the second end of the piston to a chamberformed between the first open end of the piston and the cylindricalhousing. The other of the ports leads from an interior chamber formedbetween an exterior wall of the piston and the sleeve formed by thehousing toward the second open end of the piston. One or the other ofthe ports in the body sequentially registers with the metered openingsin the feed tube when the reciprocating piston is moved into alignmenttherewith during an operating cycle of the apparatus. The second end ofthe piston body further forms a longitudinal sleeve therein.

A hammer bit body is slidably contained within a cylindrical sleeveformed by the second end of the cylindrical housing. The bit body formsa first upstream shaft end adapted to slidably engage the sleeve or boreformed in the bottom portion of the piston. Means are formed between theshaft of the bit and the bore of the piston to slideably key the shaftto the piston so that the bit rotates with the piston. The hammer bitbody further forms a second, bit cutter end.

A clutch means is contained within the housing and is positionedadjacent to and interconnected with the helical groove formed in thefirst end of the piston. The clutch mean serves to rotate the piston andthe bit keyed thereto, incrementally each time the piston reciprocateswithin the cylindrical housing during operation of the air percussionapparatus.

An advantage then of the present invention over the prior art hammertools is the ability to rotate the bit independent of any rotation ofthe drillstring.

Yet another advantage of the present invention over the prior art is theuse of an air hammer bit in a directional drilling operation.

The above noted objects and advantages of the present invention will bemore fully understood upon a study of the following description inconjunction with the detailed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the steerable hammer mechanism andbit connected to a drill string which may be part of a bent housingsubassembly;

FIG. 2 is a perspective view of the hammer drive piston illustrating thehelix grooves formed in the top section of the piston and the variouspneumatic ports formed therein;

FIG. 3 is a cross-sectional view of the hammer mechanism with the bitcutter end contacting the formation, the piston being at the top of itsstroke;

FIG. 4 is a section taken through 4--4 of FIG. 1 illustrating the innerand outer air passages formed by the hammer bit body;

FIG. 5 is a section taken through 5--5 of FIG. 3 showing therelationship formed between the bit body and the shank of the hammerbit;

FIG. 6 is a section taken through 6--6 of FIG. 3 illustrating the clutchmechanism including the helical groove and ball engaging system thatresults in bit rotary motion converted from piston reciprocating motion,

FIG. 7 is a section taken through 7--7 of FIG. 3 illustrating the spragshoused within the clutch that prevent the piston from oscillating; theclutch mechanism insures that the piston always rotates in acounterclockwise direction.

FIG. 8 is a cross-sectional view of the percussion mechanism at thetermination of one complete cycle;

FIG. 9 is a partially cutaway view of an alternative embodiment of thehammer rotary drive means, and

FIG. 10 is a view taken through 10--10 of FIG. 9 illustrating thesliding ball track mechanism between the piston and the hammer bit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE FOR CARRYING OUTTHE INVENTION

FIG. 1 illustrates an air percussion drilling assembly generallydesignated as 10. The air percussion apparatus consists of a cylindricalhousing 12 that forms an upstream threaded female end 14 adapted to beconnected to, for example, a drill string 15. The drill string mayconsists of a bent housing subassembly utilized in a directionaldrilling operation (not shown). A hammer bit generally designated as 18is slideably retained within the opposite or downstream end 16 ofcylindrical housing 12.

A check valve 20 is retained within housing 12 adjacent threaded end 14.Valve body 21 is biased closed by valve spring 22 when the percussionapparatus is not functioning or the apparatus is "tripped" out of theborehole to prevent water or formation detritus from backing up thedrill string.

A pneumatic feed tube generally designated as 24, is mounted within afeed tube support member 25; the support member being secured withinhousing 12. An interior chamber 28 communicates with the drill string 15at an upstream end of the housing 12 and with slotted, axially alignedopenings 26 formed in the feed tube wall at an opposite end of the tube24. A choke 27 substantially closes off the downstream end of the tubejust below the slotted openings 26.

A pneumatic piston generally designated as 30 slideably engages cylinderwall 13 formed by housing 12. The body 31 of the piston 30 forms anupper, reduced diameter cylindrical segment 32. An inner cylindricalwall 33 overlaps and partially engages the outside wall 29 of theconcentric feed tube 24. An annular chamber 35 formed by segment 32provides a pneumatic conduit for pressurized air to the slots 26 formedin feed tube 24 depending upon the axial position of the piston 30within housing 12. The piston body 31 further forms ports or conduits 38and 39 that communicate with slots 26 in tube 24. The ports directpressurized air either to slots 40 formed in the piston 30 and fromthere to chamber 41 formed below piston 30 in housing 12 or to annularchamber 37 above the piston depending on the axial position of thepiston as the mechanism cycles through its operating modes (see FIGS. 1and 2).

FIG. 1 illustrates the hammer bit 18 positioned above a borehole bottom8; the bit being suspended from retaining ring 49 attached to wall 13near the bottom of housing 12. As long as the bit remains off bottom 8,pressurized air 11 is directed down drillstring 15 into chamber 28formed in feed tube 24. The air is then directed through slots 26 toannular chamber 35 and from there to chamber 37. Ports 39 in piston 30then direct the pressurized fluid to air passage 53 formed through thecenter of hammer bit 18 then out through one or more nozzles 54 formedin the bit cutting face. The air under pressure serves to clean the rockchip debris and other detritus such as accumulated water from theborehole bottom 8 prior to commencement of further drilling operations.

As the air percussion assembly 10 is lowered down the borehole 6 formedin earthen formation 4, the bit 18 contacts bottom 8 (FIG. 3). The bit18 and piston 30 is subsequently pushed back into housing 12 a distancewherein shoulder 51 formed by the bit 18 contacts rim 16 formed byhousing 12. Upon contact air is shut off to chambers 35 and 37 when thepiston moves over the fixed feed tube 24. The pressurized air is thenredirected down through ports 38 to slotted channels 40 into chamber 41below piston 30. The piston is then forcibly accelerated up cylinderwalls 13 separating the impact surface 34 formed at the bottom of thepiston from the top of the hammer bit 18 as illustrated in FIG. 1. Themomentum of the piston mass carries the piston 30 to the upper end ofchamber 37. Pressurized air is then redirected to the top of the piston(chamber 37) through slots 26 in feed tube 24 into piston ports 39. Thepiston then is accelerated down cylinder walls 13; end 34 of the pistonsubsequently impacting end 55 of the hammer bit 18 thereby completingthe cycle (FIG. 8).

FIG. 3 depicts the piston 30 at the top of its travel within cylindricalsleeve 13 prior to being accelerated toward impact surface 55 of hammerbit 18. As the piston moves downward toward the hammer bit, the clutchmechanism generally designated as 56, engages ball 58 with helicalgroove 36 formed in the upper reduced diameter section 32 of piston 30.The piston moves in a clockwise direction as it moves down toward thehammer bit and, since the hammer bit is keyed to the piston, the bitmoves rotationally in concert with the piston. When the piston is cycledin the reverse or upward direction, the clutch slips hence preventingthe piston (and hammer bit) from rotating in a counter clockwisedirection. The piston and hammer bit therefore is rotationally indexedin a clockwise direction only.

The piston and hammer is preferably rotated on the downstroke of thepiston for the following reasons; there is tremendous formationresistance imparted to the piston hammer mechanism on the upward cycleof the piston due to the fact that the lower chamber 41 is chargedforcing impact surfaces 34 and 55 apart subsequently driving the cuttingface 19 of the hammer bit into the formation thereby resisting theturning or rotational force exerted on the piston by the ball 58 inhelical groove 36. Therefore, if the rotational forces were exerted onthe piston and the bit on the downstroke, the bit is released from theformation and the rotational forces easily rotate or index the bit toits new position without unnecessary wear on the various slidingsurfaces.

FIG. 4 illustrates a section taken through housing 12 (FIG. 1) showingthe piston 30 with the shaft 50 of the hammer 18 slideably retainedwithin sleeve 42 formed by the piston. The rectangular shaped shaft 50with rounded ends, for example, is slideably retained withincomplimentarily shaped sleeve 42 formed in piston 30. The central airpassage 53 communicates with the nozzles 54 formed in the cutter face 19of hammer 18.

It would be obvious to utilize conventional hammer bit splines as ameans to key the shank of the hammer bit to the piston without departingfrom the scope of this invention.

FIG. 5 depicts a section through the hammer body 47 slideably retainedin cylindrical sleeve 17 fastened to the lower housing 12. Air passages52 in the body 47 allow air under pressure to escape around the hammerbody when the apparatus 10 is suspended above the borehole bottom 8(FIG. 1). As heretofore mentioned, a free flow of air prevents debris(and water) from contaminating the air percussion apparatus while themechanism is being tripped in and out of the borehole.

FIG. 6 details part of the clutch mechanism 56. This view locates thehelical groove engaging balls 58 at the bottom of the helix 36 in shank32 of piston 30 (FIG. 3). The balls 58 are retained in ball race 59; therace 59 being secured within ball and clutch housing 60.

FIG. 7 is a view taken through the clutch mechanism primarily comprisedof a multiplicity of "sprags" or clutch dogs 57 that allow rotation inone direction only. Since rotation preferably occurs only on the pistondownstroke, the clutch dogs 57 engage the balls within helical tracks 36resulting in a clockwise rotation of the piston and hammer bit asheretofore described. On the upstroke of the piston the clutch releasesthe ball driver mechanism. The piston then travels up the housing 12without rotation.

FIG. 8 illustrates the percussion tool 10 at the completion of anoperating cycle. The hammer has been rotated or indexed the preferred 4to 5 degrees prior to impact of the cutting face 19 of the hammer bitwith the formation bottom 8. Since the hammer bit rotates independent ofthe drill string, it does not matter whether the drill string rotates ornot hence the air percussion tool is ideal for directional drillingoperations wherein a bent housing subassembly is normally incorporated.

FIG. 9 is an alternative piston shank sliding engagement mechanism. Thepiston 130 forms an internal sleeve 142 with, for example, threeparallel, axially aligned semi-circular grooves 120 degrees apart formedin the sleeve wall of the body. The shank 150 of hammer bit 118 retainsthree ball bearings 160 that are aligned with each of the complimentarygrooves 143 formed in the piston body 131. The shank of the hammer bitthen is slideably "splined" to the piston with a minimum of drag.

The cross-section of FIG. 10 depicts the ball bearings 160 secured tothe shank 150 of the hammer bit 118 and slideably engaged with theparallel grooves 143 formed in the piston body 131.

It will of course be realized that various modifications can be made inthe design and operation of the present invention without departing fromthe spirit thereof. Thus, while the principal preferred construction andmode of operation of the invention have been explained in what is nowconsidered to represent its best embodiments, which have beenillustrated and described, it should be understood that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically illustrated and described.

What is claimed is:
 1. An air percussion hammer apparatus fordirectional drilling operations with means for rotating the hammer bitwhile it reciprocates in a housing independent of an attached drillstring, said bit rotating means comprising:a cylindrical housing forminga first open up-stream end connectable to a drill string component and asecond downstream end, said second end containing said hammer bit, apneumatic feed tube forming a first open end and second substantiallyclosed end, said first end of the feed tube is concentric with and fixedwithin said housing and positioned toward said first up-stream end ofsaid housing, the second end of the feed tube forms one or more meteredopenings between said first and second ends of the feed tube, a pistonbody is slidably retained within a first cylindrical sleeve formed bysaid cylindrical housing, the piston body forms a first open upstreamend and a second open downstream end, said first open upstream end isreduced in diameter, inner walls formed by said first open upstream endfurther concentrically contains said second end of said feed tube, saidinner walls of said first open upstream end being slidably engaged withan outside surface formed by said second end of said feed tube, saidsecond downstream end of said piston body engaged with said firstcylindrical sleeve forms a hammer striking surface, said piston bodyfurther forms at least one axially oriented helical groove in an outsidewall formed by said reduced diameter first open upstream end of saidpiston body and at least a pair of pneumatic communication ports betweenan outside wall of said piston body positioned between said first openupstream end and said second open downstream end of said piston body andan interior chamber formed by said piston body, one of said ports leadsfrom said interior chamber formed by said piston body to a chamberformed between said outside wall of the first open upstream end of thepiston body and said first cylindrical sleeve, the other of said portsleads from an interior chamber formed within the first open upstream endof the piston body through a port formed by said piston body to saidfirst cylindrical sleeve adjacent thereto, one or the other of saidports in said body sequentially registers with said metered openings insaid feed tube when said reciprocating piston is moved into alignmenttherewith during an operating cycle of said apparatus, said second opendownstream end of the piston body further forms a longitudinallyextended sleeve concentrically therein, a hammer bit body is slidablycontained within a second sleeve formed by said second end of saidcylindrical housing, said hammer bit body further forms an upstreamshaft end adapted to be axially slidable within said sleeve formed insaid second open downstream end of said piston body, said shaft end ofsaid hammer is rotationally keyed to said piston body by an engagementmeans such that the hammer bit moves in concert with said piston, saidbit body forming a second downstream cutter end, and clutch meanscontained within said housing, said clutch means being positionedadjacent to and interconnected with said at least one helical grooveformed in said first reduced diameter open upstream end of said pistonbody, the clutch means serves to rotate the piston body and the hammerbit body engaged therewith incrementally and in one direction only, eachtime the piston body oscillates within the cylindrical housing duringoperation of the air percussion hammer apparatus.
 2. The invention asset forth in claim 1 wherein said engagement means that slidably keysthe upstream shaft end of said hammer bit body to said sleeve formed bysaid second open downstream end of the piston body comprises at least apair of longitudinally extending, oppositely opposed flats formed bysaid shaft end, said second open downstream end of the piston bodyforming complimentary flats to slidably accept said shaft within saidsleeve.
 3. The invention as set forth in claim 1 wherein said engagementmeans comprises at least a pair of spherically shaped detents slidablyengaged with complimentary shaped, longitudinally extending groovesformed in adjacent surfaces of said upstream shaft end of said hammerand said sleeve formed in said piston.
 4. The invention as set forth inclaim 3 wherein there are three spherically shaped detents connected toand extending from said upstream end of said shank of said hammer, saiddetents being positioned about 120 degrees apart, said detents beingslidably engaged with complimentary shaped longitudinally extendinggrooves formed in an inner wall of said sleeve formed by said secondopen downstream end of the piston body.
 5. The invention as set forth inclaim 1 wherein said engagement means comprises a multiplicity oflongitudinally extending splines formed by said shank of said hammerbit, said splines being slidably interfitted with splines formed by saidsecond open downstream end of the piston body in a wall of said sleevetherein.
 6. The invention as set forth in claim 1 wherein said pistonbody and hammer bit is rotated by said clutch means when said pistonbody moves toward said second open downstream end of said cylindricalhousing.
 7. The invention as set forth in claim 1 wherein the rotationalspeed of the piston and hammer is between 10 and 20 RPM.
 8. Theinvention as set forth in claim 7 wherein the rotational speed is about20 RPM.
 9. The invention as set forth in claim 1 wherein the hammer bitimpacts an earthen formation during operation of the air percussionapparatus about 1600 strokes of said reciprocating piston body andhammer bit per minute.
 10. The invention as set forth in claim 9 whereinthe rotational speed of the piston and hammer results in a rotationaldisplacement of the hammer bit with respect to said cylindrical housingof about 5 degrees per each impact of the bit against the formation. 11.The invention as set forth in claim 1 wherein the clutch means is asprag clutch.
 12. The invention as set forth in claim 11 wherein thesprag clutch allows the piston and hammer to rotate on the downstrokeonly, the clutch releases on an upward cycle of the piston body whensaid piston body moves toward said first open upstream end of saidcylindrical housing.
 13. The invention as sets forth in claim 11 whereinthe clutch is engaged with the helical groove formed in said reduceddiameter first open upstream end of the piston body by a ball bearingsecured to said clutch, said helical groove being circular in crosssection to match the circumference of the ball bearing engagedtherewith.
 14. The invention as set forth in claim 12 wherein there arethree helical grooves formed in said first open upstream end of thepiston body 120 degrees apart, each of said grooves is engaged with saidball bearing retained within said clutch means.
 15. An air percussionhammer apparatus for directional drilling operations comprising:acylindrical housing having an upstream end connectable to a drill stringcomponent and a downstream end including means for mounting a hammerbit; a piston slidably retained within the housing, a downstream end ofthe piston including a surface for striking a hammer bit mounted on theend of the housing; fluid porting in the housing for alternately drivingthe piston upwardly in the housing and driving the piston downwardly inthe housing for striking a hammer bit; means for rotating the pistonduring the downward stroke of the piston; means for preventing rotationof the piston during the upward stroke of the piston; and keying meansfor permitting relative longitudinal movement while preventing relativerotation between the hammer bit and the piston.
 16. The invention as setforth in claim 15 wherein the hammer bit is mounted for reciprocalmovement in the housing and characterized by means for venting fluidfrom the hammer when the hammer bit is relatively down in the housingand for applying fluid pressure for driving the piston when the hammerbit is relatively up in the housing.
 17. The invention as set forth inclaim 15 wherein the hammer bit is slidably contained within thedownstream end of the cylindrical housing, the hammer bit comprising anupstream shaft end axially slidable within the piston, the shaft end ofthe hammer being rotationally keyed to the piston by an engagement meanssuch that the hammer bit rotates in concert with the piston.
 18. Theinvention as set forth in claim 17 wherein the clutch means comprises atleast a pair of spherically shaped detents for slidably engagingcomplementary shaped helical grooves in the upstream end of the piston.19. The invention as set forth in claim 15 wherein the keying means forpermitting relative longitudinal movement while preventing relativerotation between the hammer bit and the piston comprises threespherically shaped detents between the upstream end of the shank of thehammer and the inside of the piston, the detents being positioned about120 degrees apart and slidably engaged with complementary shapedlongitudinally extending grooves.
 20. The invention as set forth inclaim 15 wherein the means for rotating the piston during the downwardstroke of the piston comprises a helical groove in the piston with ahelix angle and length sufficient for rotating the piston approximatelyfive degrees per cycle of the piston.
 21. The invention as set forth inclaim 15 wherein the means for rotating the piston during the downwardstroke of the piston comprises a helical groove in the piston and a ballbearing engaging the housing and the helical groove.
 22. The inventionas set forth in claim 21 wherein there are three helical grooves formedin the upstream end of the piston 120 degrees apart, each of the groovesbeing engaged with a ball bearing retained within the housing.
 23. Amethod of rotating a hammer rock bit of an air percussion hammer bitapparatus for directional drilling operations while it reciprocates in ahousing, the rotation of the bit being independent of an attached drillstring comprising the steps of;forming a cylindrical housing an openupstream end connectable to a drill string component and a downstreamend containing a hammer bit, the hammer bit being free to reciprocatelongitudinally in the housing; mounting a longitudinally moveableannular piston on the housing defining a first chamber having anupstream end and a downstream end having a hammer striking surface, andincluding a helical groove in an outside wall of the piston; alternatelypassing air from a chamber above the upstream end of the piston to theinside of the piston, and passing air from the inside of the piston to achamber outside of the piston adjacent to the downstream end of thepiston, for reciprocating the piston in the housing and striking thehammer bit; engaging the helical groove with a detent for rotating thepiston during a downward stroke of the piston; rotating the hammer bitin concert with the piston; and preventing rotation of the piston duringan upward stroke of the piston. .Iadd.
 24. A component for a bottomholeassembly used for directional drilling in an underground borehole, theassembly having a bend and one or more stabilizers comprising:a housinghaving an up-stream end associated with a drill string and a downstreamend associated with a drill bit; a reciprocating member slidably mountedwithin the housing, the reciprocating member being movable upwardly anddownwardly within the housing and having an impact surface for strikingthe drill bit; and means within the housing for cooperatively rotatingthe reciprocating member and the drill bit independent of movement ofthe housing, and independent of movement of the drill string..Iaddend..Iadd.
 25. A component for a steerable bottomhole assembly, theassembly having a bend and one or more concentric stabilizerscomprising:a housing having an upstream end connectable with a drillstring and a downstream end; a reciprocating piston slidably retainedand movable upwardly and downwardly within the housing, the pistonhaving an impact surface for striking a drill bit; and a clutch thatpermits rotation of the piston independent of rotation of the housing..Iaddend..Iadd.26. A component for a bottomhole assembly used fordirectional drilling in an underground borehole, the assembly having abend and one or more stabilizers comprising: a housing having anupstream end connectable to a drill string and a downstream end; areciprocating piston slidably retained and movable upwardly anddownwardly within the housing, the piston having an impact surface forstriking a drill bit; and a clutch that permits rotation of the pistonindependent of rotation of the drill string. .Iaddend..Iadd.27. Acomponent for a steerable bottomhole assembly for controlled drilling ofa borehole, the assembly having an upstream end connected with a drillstring, wherein the drill string is rotatable from the surfacecomprising: a housing having an up-stream end associated with a drillstring and a downstream end associated with a drill bit; a reciprocatingmember slidably mounted within the housing and moveable upwardly anddownwardly within the housing, the reciprocating member having an impactsurface for striking the drill bit; and means for cooperatively rotatingthe reciprocating member and drill bit independent of movement of thehousing, and independent of movement of the drill string..Iaddend..Iadd.28. A component for a directional drilling assembly, theassembly including a bend and one or more concentric stabilizers andhaving an upstream end connectable with a drill string comprising:ahousing; a piston slidably retained within the housing; fluid porting inthe housing allowing the piston to be driven upwardly and downwardly inthe housing; means for rotating the piston during the downward stroke ofthe piston; means for preventing rotation of the piston during theupward stroke of the piston; and keying means for permitting relativelongitudinal movement while preventing relative rotation between ahammer bit and the piston. .Iaddend..Iadd.29. A method for directionaldrilling of a borehole with a bottomhole assembly having an upstream endconnected with a drill string, the drill string being rotatable from thesurface, wherein the bottomhole assembly further includes a drill bitand a housing containing a reciprocating piston, comprising:associatingthe piston and drill bit to allow cooperative rotation of the piston anddrill bit; reciprocating the piston in the housing; rotating the pistonin the housing; rotating the drill bit in concert with the piston; andrestraining rotation of the drill string. .Iaddend..Iadd.30. A methodfor controlled directional drilling of a borehole utilizing a drillingsystem, the drilling system including a rotatable drill string and abottomhole assembly, the bottomhole assembly having an upsteam endconnectable to the drill string for cooperative movement therewith, thebottomhole assembly further having a bend and a drilling hammer, thedrilling hammer including a rotatable piston capable of impacting adrill bit, the piston and drill bit associated for cooperative rotationindependent from rotation of the drill string, comprising: drilling atan angle by rotating the piston of the drilling hammer and restrainingrotation of the drill string; and drilling in a straight direction byrotating both the piston of the drilling hammer and the drill string..Iaddend..Iadd.31. A method for controlled directional drilling of aborehole utilizing a drilling system, the drilling system including arotatable drill string and a bottomhole assembly, the bottomholeassembly having an upsteam end connectable to the drill string forcooperative movement therewith, the bottomhole assembly further having abend and a drilling hammer, the drilling hammer including a rotatablepiston capable of impacting a drill bit, the piston and drill bitassociated for cooperative rotation independent from rotation of thedrill string, comprising:steering the bottomhole assembly by activatingthe drilling hammer and selectively rotating the drill string..Iaddend..Iadd.32. A bottomhole assembly for directional drilling, thebottomhole assembly comprising: a housing having an upstream endconnectable to a drill string and a downstream end, the housing beinginsertable into an underground borehole; a reciprocating piston slidablyretained and movable upwardly and downwardly within the housing, thereciprocating piston having an impact surface for striking a drill bit;and at least one helical groove allowing rotation of the pistonindependent of rotation of the housing. .Iaddend..Iadd.33. A bottomholeassembly for directional drilling, the bottomhole assembly comprising: ahousing having an upstream end connectable to a drill string and adownstream end, the housing being insertable into an undergroundborehole; a reciprocating piston slidably retained and movable upwardlyand downwardly within the housing, the reciprocating piston having acylindrical outer surface and an impact surface for striking a drillbit; and at least one helical groove formed on the cylindrical outersurface of the piston and allowing rotation of the piston independent ofrotation of the drill string. .Iaddend..Iadd.34. A component for adirectional drilling assembly, the assembly including a bend,comprising:a housing having an upstream end connectable to a drillstring and being insertable into an underground borehole; a pistonslidably mounted within the housing, the piston moveable upwardly anddownwardly within the housing and rotatable within the housing; thepiston engaging a shaft; a key engaging the piston and the shaft and forallowing cooperative rotational movement of the piston and the shaft;and the key including at least one ball and at least one groove..Iaddend.